Spin Accelerating Mechanism for Gyroscopic Wave Energy Converter

This paper describes a spin accelerating mechanism by precession rotation designed for a gyroscopic generator. A gyroscopic generator is a type of energy harvesting system that extracts vibration energy in the environment via the inertial force of the weight. By using the gyroscopic effect, more power can be obtained from a weight of the same mass. Ocean monitoring using smart buoys has been actively conducted, but the primary batteries installed have a service life of about only one month and regular battery replacement work is required. There is a problem that maintenance work is difficult because buoys have a total weight of more than 20 kg. Solar cells and wave power generation have been studied to replace primary batteries but have not obtained enough power. In the case of wave power generation, marine waves have a low frequency, so that conventional generators that use a simple vibration of the weight can hardly obtain energy. For this reason, gyroscopic generators have been developed. However, typical gyroscopic generators have low power generation efficiency because they generate power by low speed precession rotation. With a flywheel of about 10kg that can be mounted on a smart buoy, there is a problem that the amount of power generation is less than the energy required to maintain spin speed. This means that the generator does not function as a generator. A friction-driven gyroscopic generator that generates power by high speed spin rotation for high efficiency power generation has been developed, but it has problems such as energy loss due to slippage and frequent maintenance due to wear of friction parts.

In this study, a new mechanism to increase the speed by transmitting precession torque mechanically to the rotating shaft in order to realize high efficiency power generation by high speed spin rotation for the realization of a gyroscopic generator mounted on a smart buoy is proposed. This mechanism mainly consists of an inner gimbal that supports the flywheel to rotate only around the spin axis and an outer gimbal that supports the inner gimbal to rotate only around the precession axis perpendicular to the spin axis. When rotational vibration is applied around an axis in a direction different from that of both the spin axis and the precession axis, precession torque is generated, and the inner gimbal and flywheel rotate around the precession axis. The relative motion between the inner gimbal and outer gimbal generated at this time is taken out and the gears are rotated. Furthermore, the direction of the rotating shaft is changed using a bevel gear from rotation around the precession axis to rotation around the spin axis, and the speed is increased by a gear train to fill the difference between the precession rotation speed and the spin speed. In order to ensure that the rotation is always accelerated in a fixed direction regardless of the direction of precession rotation, two one-way clutches are used to mechanically control the transmission of torque.

A gyroscopic power generator using this mechanism and using a small flywheel with a diameter of 100 mm was prototyped. An experiment was conducted in which a rotating vibration with an amplitude of 90 degrees for 1 second was applied by a shaker while extracting energy from the generator with load resistance. It was confirmed that the spinning speed increased due to the precession torque, and the flywheel eventually rotated at a speed exceeding 1000 rpm.